depends on the year on the dmaxs. 04.5 and newer are all turbo noise hardly any motor noise, probably the hoover vacuum sound u speak of. 01-04 lb7 are all motor sounds and can't even tell they have a turbo, they sound pretty bad a$$ when hooked to a sled. some of the older fords sound alright under load to. i have an 05 dmax straight piped and its not loud but it is all turbo sound, sounds like a jet. I've never been partial to the sound of the inline engines but to each their own.